Instead of a single mirror, telescopes of the newer generation have a plurality—up to a few thousand—of mostly hexagonal mirror segments. Normally, all mirror segments are fixed in place in a densely packed manner in a hexagonal arrangement, so that, with the exception of edge mirror segments, mirror edges of adjacent mirror segments are always positioned parallel to each other at a clearance of approximately 1 mm. If the telescopes are to be able to carry out their imaging tasks, the position of the mirror segments relative to each other must be controlled very precisely. Segmented telescopes often have an extremely large overall surface and are typically installed out in the open.
PCT International Published Patent Application No. WO 2004/020953 describes a measuring device for determining the relative positions of corresponding mirror segments, which is based on a capacitive operating principle. The sensitive elements are secured to the end faces of the mirror segments. One of the disadvantages of such measuring systems is their relatively low measuring sensitivity, so that they are generally considered unsuitable for applications requiring high measuring accuracy. Furthermore, the measurement is influenced considerably by fluctuations in the air humidity and by small condensation droplets. In addition, these systems provide different signal amplitudes as a function of the particular clearance or gap between adjacent mirror segments. Furthermore, in conventional measuring systems, the sensors must be disposed within the small gap between the mirror segments, which is possible only if the gaps have a correspondingly large size. This has a considerable detrimental effect on the optical transfer function and the quality of the telescope.
European Patent No. 1 379 832 describes a measuring probe, which has a pin having a point-shaped probe geometry, the pin being guided inside the housing of the measuring probe. Such measuring probes may also be operated side-by-side. However, systems of this type cannot offer the accuracy that is required, for example, in measuring the relative offset of adjacent mirror segments in telescopes.